EST/PST? Are they released at the same official time each Wednesday, or does it vary? If it does, what time are they generally released? Looking for a definitive source.
From Wikipedia it seems a vast majority of the games were released on Wednesdays, at least for the sampling of about 10 released in 2012 that I checked. I do note that this is not an absolute rule, as a game ironically named "Anomaly: Warzone Earth" was released on April 6th, 2012 - a Friday. Unless that is an error, which would in turn be even more ironic.
From Major Nelson's blog it appears that he posts updates about Arcade games around ~6 AM PST on release days most of the time. I think this is about the best info you are likely to get and there's no way to be sure it will stay that way. Also note that all games state "Check availability in your Xbox Live region", which means that while this info is probably accurate for US, times may vary by hours or days for other regions.
XBLA games are usually released 12:00 PM UK time (GMT 0) and are available after that.
If you live in the States, i would expect the time to be around 12:00 PST but im not as sure as the Europe timing.
Some games may be released on other days of the week, (such as the game FEZ which was released last friday)
Hope i was some kind of help and cheers ;)
I have actually called Microsoft to find out what time the Resident Evil 4 HD would be released, and was told "at some point during the release date". My buddy that keeps the sleep schedule of an owl told me that he was able to buy it at 4 AM CST on its release date, but have heard generally between midnight and 6 am depending on time zones among many other undisclosed factors.